The present invention relates to a display circuit of an electronic filing apparatus having an optical disk, and more particularly to an image information display apparatus suitable for providing man-machine interface adapted for a high speed code expander.
When image data is displayed on a display of the electronic filing system, by using a display circuit having only one image memory as is the case in a conventional computer, an operator sees on the display a process of sequential overwriting of new image data on previous image data because of a low speed of code data expansion. Thus, the operator sees as if a leading edge of the image data under transfer repeatedly moves vertically from one line to other line on the display, and if the operators watch it, many of them have the uncomfortable feeling like light seasickness.
As means for solving the above problem, an apparatus disclosed in JP-A-59-26787 has been proposed.
FIG. 2 shows a simplified block diagram of a prior art apparatus. Numeral 21 denotes an optical disk which stores image data to be displayed, in a compressed status (code data); numeral 22 denotes a code expander for converting the code data to image data; numeral 23 denotes a selector for selecting one of two image memories in which the image data is to be written; numerals 24 and 25 denote image memories for storing the image data for display; numeral 26 denotes a selector for selecting one of the image data stored in the two image memories; which is to be displayed, numeral 27 denotes a timing signal generator for generating a horizontal synchronization signal and a vertical synchronization signal; numeral 28 denotes a CRT for displaying the image data in accordance with the timing signals; numeral 29 denotes an end of writing flag for indicating the end of conversion of the image data by the code expander 22 for each screen; and numeral 30 denotes an inverter for operating the two selectors 23 and 26 in the opposite phases.
The operation of the apparatus is now explained. The code data stored in the optical disk 21 is first read, and it is supplied to the code expander 22. In the code expander 22, the code data is decoded in accordance with an encoding rule, and it is converted into image data. The converted image data is supplied through the selector 23 to one of the two image memories 24 and 25 from which data is not outputted to the CRT 28.
On the other hand, the code expander 22 generates an end signal each time the process of the screen is finished, and supplies it to the end of writing flag 29. The end of writing flag 29 operates as a toggle switch, and it switches each time the process of one screen is completed. An output signal of the end of writing flag 29 is supplied to the selector 26 through the selector 23 and the inverter 30. The signal inverted by the inverter 30 is supplied to the two selectors 23 and 26 so that the two image memories 24 and 25 are allotted to writing and reading for each screen.
The image data is supplied from the read image memory 24 or 25 to the CRT through the selector 26. The CRT 28 displays the image data in accordance with the horizontal synchronization signal and the vertical synchronization signal supplied from the timing signal generator 27.
In the prior art apparatus described above, two image memories for storing the image data are alternately switched to display the image data.
Thus, even in an electronic filing apparatus having a low code expansion speed, the operator does not see if the leading line of the image data under transfer repeats the vertical movement, and the operator may continue paging without having the uncomfortable feeling.
In the prior art apparatus, however, since the end of one-screen processing signal of the code expander is used to switch the display screen, the screen switching time of the image data is determined by the code expansion time for one screen. As a result, independently of a response of the operator, the screen switching period is short if the expansion processing speed for the image data is high, and the switching period is long if the processing speed is low.
On the other hand, turning to the response of the operator to the display screen, it varies from two times to four times of a recognition time, depending on an individual. FIG. 3 shows a relation between a presentation time of the image data and an identification factor, and FIG. 4 shows a distribution of response times of operators to the image data. (M. Suzuki et al, "Study on Identification/Response Characteristic in High Speed Image Retrieval", The Institute of Electronics, Information and Communication Engineers (IEICE) Technical Report OS86-18, pp. 83-89, 1986). As seen from FIG. 3, approximately 0.2 second is required for the operator to recognize the display screen, and the time for recognition is independent of the complexity of the screen so long as the screen images are of the same type. Accordingly, an ideal screen switching period in the electronic filing apparatus is approximately 0.2 second. On the other hand, the response times are distributed between 0.2 second and 1.0 second and are concentrated between 0.4 second and 0.6 second. Thus, the response time is 2 to 3 times, or five times in an extreme case, as large as the recognition time. It is anticipated that the value may be somewhat higher when factors of working attitude and fatigue are taken into consideration. Accordingly, the response time is up to six times as large as the recognition time, depending on an individual.
In many of the existing electronic filing apparatus, the screen switching time is around two seconds, and even in a high performance apparatus, it is around one second. Accordingly, the display screen switching time is longer than the response time of the operator, and an overrun in which several screens have already been switched when the operator responses does not occur. However, the processing speed of the code expander has been increased year by year with the advancement of the image processing technology and the LSI technology, and it is now not impossible to attain the screen switching time of 0.2 second which is an ideal time.
Thus, as the code expansion speed is increased in the prior art apparatus which pays no attention to an overrun correction function in screen switching (screen paging) operation, the display screen may stop after several screens have been switched when the operator responses to stop the paging.
When the paging speed is increased as the LSI technology advances and the image processing speed is increased, an image information display apparatus which can flexibly comply with the overrun of the display screen due to the difference between the recognition time and the response time of the operator is required.